1. Field of the Invention
Embodiments of the present invention generally relate to methods for improving interface adhesion. More particularly, embodiments of the present invention relate to interface adhesion improvement methods performed on a surface of a substrate used in thin-film transistor or OLED applications.
2. Description of the Related Art
Organic light emitting diode (OLED) displays have gained significant interest recently in display applications in view of their faster response times, larger viewing angles, higher contrast, lighter weight, lower power and amenability to flexible substrates. Generally, a conventional OLED is enabled by using one or more layers of organic materials sandwiched between two electrodes for emitting light. The one or more layers of organic materials include one layer capable of monopolar (hole) transport and another layer for electroluminescence and thus lower the required operating voltage for OLED display.
In addition to organic materials used in OLED, many polymer materials are also developed for small molecule, flexible organic light emitting diode (FOLED) and polymer light emitting diode (PLED) displays. Many of these organic and polymer materials are flexible for the fabrication of complex, multi-layer devices on a range of substrates, making them ideal for various transparent multi-color display applications, such as thin flat panel display (FPD), electrically pumped organic laser, and organic optical amplifier.
Over the years, layers in display devices have evolved into multiple layers with each layer serving different function. FIG. 1 depicts an example of an OLED device structure 100 built on a substrate 102. The OLED device structure 100 includes an anode layer 104 deposited on the substrate 102. The substrate 102 may be made of glass or plastic, such as polyethyleneterephthalate (PET) or polyethyleneterephthalate (PEN). An example of the anode layer 104 is an indium-tin-oxide (ITO).
Multiple layers of organic or polymer materials 106 may be deposited on the anode layer 104. Multiple layers of organic or polymer materials 106 may generally include a hole-transport layer and an emissive layer. Different organic materials may be used to fabricate the hole-transport layer and the emissive layer. Suitable examples of the hole-transport layer may be fabricated from diamine, such as a naphthyl-substituted benzidine (NPB) derivative, or N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD). Additionally, suitable examples of the emissive layer may be fabricated from 8-hydroxyquinoline aluminum (Alq3). Subsequently, an electrode layer 108 or called cathode layer may be formed on the organic or polymer materials 106 to complete the device structure 100. The electrode layer 108 can be a metal, a mixture of metals or an alloy of metals. An example of the top electrode material is an alloy of magnesium (Mg), silver (Ag) and aluminum (Al) in the thickness range of about 1000 Å to about 3000 Å. The structure of the organic or polymer materials 106 and the choice of anode and cathode layers 104, 108 are designed to maximize the recombination process in the emissive layer, thus maximizing the light output from the OLED devices.
After the device structure 100 is formed on the substrate 102, a first barrier layer 111 followed by an encapsulating planarization layer 110 formed thereon. Subsequently, a second encapsulating barrier layer 112 is formed thereon. Additional passivation layers 116, 118 may be formed on the encapsulating barrier layer 112 as needed to provide sealing of the device structure 100 from moisture or air exposure. However, different materials, especially organic and inorganic materials, often have different film properties, thereby resulting in poor surface adhesion at the interface where the organic and the inorganic layers are in contact with. For example, poor adhesion is often present at an interface 114 formed between the first encapsulating planarization layer 110 and the second encapsulating barrier layer 112 (or the interface between the first encapsulating barrier layer 111 and the first encapsulating planarization layer 110). Poor interface adhesion often allows film peeling or particle generation, thereby adversely contaminating the device structure 100 and eventually leading to device failure. Additionally, poor adhesion at the interface 114 may also increase the likelihood of film cracking, thereby allowing the moisture or air to sneak into the device structure 100, thereby deteriorating the device electrical performance.
Thus, there is a need for methods to form an interface with different materials with good adhesion while maintaining good passivation capability to prevent device structure from moisture.